1. Field
The following description relates to a technology of locating a sensor node in a sensor network, and more particularly, to a sensor node having a self localization function and a self localization method thereof.
2. Description of the Related Art
In order to enhance the value of sensing data in most applications of sensor networks, it is very important to recognize a location of all sensor nodes. Conventional localization schemes of a sensor network are mainly divided into a ranging based localization and a ranging-free localization. The former is a performed by measuring a distance between an anchor node indicating a location through a received signal strength indicator (RSSI) or a time of arrival (ToA) and a sensor node and then performing a self localization by using locations of at least three anchor nodes and distances between the anchor nodes. The latter is performed by using an approximate distance difference and communication connectivity between an anchor node and a sensor node.
However, when a distance between the anchor node and a sensor node is measured using the RSSI, a great amount of distance error occurs, and thus localization error is increased. For this reason, in order to precisely measure a distance, additional equipment such as ultrasonic wave transceiver and an amplifier is necessary and high amounts of power are consumed.
In particular, if only a few anchor nodes are provided in the sensor network, the measuring of a distance between the anchor node and the sensor node requires a prediction of a multi-hop distance. As a result, the distance error is increased and thus localization error is increased. In addition, in a ranging-free localization, if the number of anchor nodes is small, localization error is increased.
However, when the initiation of a sensor network is performed, a large number of anchor nodes increases the number of GPS nodes, allowing increase in construction cost and power consumption. In addition, if a large number of anchor nodes are installed, location data needs to be manually inserted, and this thus increases the initiation cost of sensor networks. As a result, the installation cost of the sensor network is increased.
In the case of “U-city”, an example of the application of sensor networks, a network is installed outdoors, in particular in a urban area, and thereby a large number of sensor nodes are disposed to detect weather, traffic, congestion area and serve as a driver assistant system. In order to realize such urban applications, a large amount of sensor nodes are required to be installed, so additional equipment needs to be mounted on the sensor node or a large number of anchor nodes needs to be disposed, creating an increase in the initiation cost of the sensor network.
Accordingly, in the case of the urban application using the sensor network, a method of locating a sensor node at low costs need to be developed by only using a small number of anchor nodes without having to mount additional equipment on the sensor node. In this regard, a study has been pursued to provide a sensor node capable of recognizing a location of the sensor node without using an anchor node.